I'm having trouble adding the ssh key due to the bad address ssh looks for the keys. And I have no clue where to effectively change it

I got a host of troubles with the SSH key on a Windows 10 laptop, using Git Bash 64 bit. First:

Step 1.1: There is no Open SSH first line when I run ssh -v. Does this mean something?Step 1.1: "If you don't have ssh installed, install it now with your package manager." What does this mean, exactly? What is a package manager? Why should I? I never needed to do this before.

Here's what I think "the root of my problem":

Step 2.2: ssh-keygen

It will show me this:

Generating public/private rsa key pair.Enter file in which to save the key (/home/robertt/.ssh/id_rsa):

Unacceptable, Windows cannot write to that address, it makes absolutely no sense. How can I change this?

All the further troubles stem from this step alone. The problem is that ssh looks in the /home/robertt/.ssh/id_rsa, when it should look into /c/users/robertt/.ssh/id_rsa. I have no idea what variable or configuration controls this.

All my other computers show the right address and I had no trouble following the steps of the guide. But now, on this laptop, even if I mention custom addresses, I'll eventually fail at Step 5.8. And when the ssh-agent initalizes, I'm never asked of the passphrase